Mri Tracks Transplanted Islets in Mice

NEW YORK (Reuters Health) - Researchers at Harvard Medical School have developed a protocol in mice in which insulin-producing islet cells are labeled with a magnetic imaging probe that can be detected by MRI, thus representing a potential easy noninvasive way for doctors to follow islet cell transplantation in humans.

Islet cell transplantation is a promising therapy for insulin-dependent or type 1 diabetes. "Right now, all we can do to follow the fate of transplanted islet cells is monitor blood glucose," senior investigator Dr. Anna Moore told Reuters Health.

The problem with that approach, she explained, is that blood sugar "doesn't give direct information about the health of those transplanted islets."

The advantage of using a magnetic probe along with MRI is that it may detect inflammation, immune rejection, and toxicity resulting from elevated blood sugar or "hyperglycemia" without performing a biopsy, she added.

According to a report in Nature Medicine, Moore's group incubated islet cells with magnetic nanoparticles. Their testing showed that the cells' sugar-stimulated insulin secretion was unchanged, and that treatment resulted in a loss of signal on MRI images.

When treated human pancreatic islets were implanted into the kidney of mice, MRI showed a marked decrease in signal intensity on imaging at the implantation site. Moreover, the change in the image remained stable in the labeled graft over a 188-day study period.

The labeled cells were also capable of restoring normoglycemia in diabetic mice, with no difference between labeled and unlabeled islets.

Similar results were obtained when labeled islets were infused through a vein into the liver of mice. The cells were readily visualized by MRI, and normoglycemia was restored within 1 week.

"Now we are trying to see if we can obtain similar results with a contrast agent approved by the FDA for imaging of the liver," the researcher said. If all goes well, she hopes that a human trial can be started within the next year.

SOURCE: Nature Medicine, December 2005.